Flu vs. HMPV: How to Tell the Difference Between Two Easily Mistaken Respiratory Viruses

As cold and flu season stretches into spring, medical experts are sounding the alarm over another virus often mistaken for influenza: Human Metapneumovirus (HMPV). Though less well-known than the flu or COVID-19, HMPV is now being recognized as a potentially serious respiratory illness—especially in vulnerable populations—and it’s surging in some regions. What makes this tricky is that its symptoms mirror those of the flu almost exactly, leading to frequent misdiagnosis and delayed treatment.

So how can you tell the difference between HMPV and influenza? Let’s break it down.

What is HMPV, and Why Haven’t You Heard Much About It?

Discovered in 2001, Human Metapneumovirus is part of the Paramyxoviridae family—making it a cousin of the Respiratory Syncytial Virus (RSV). While HMPV has likely been circulating in humans for decades, it wasn’t until recent years that its public health impact was fully appreciated.

Today, HMPV is known to be a major cause of respiratory illness, particularly among young children, older adults, and those with weakened immune systems. Yet awareness remains low.

In a recent CDC surveillance report, HMPV detection in hospitalized patients has risen sharply, occasionally outpacing RSV and even seasonal flu in some areas during late winter and early spring.

Why It’s Often Mistaken for the Flu

HMPV and influenza both cause upper and lower respiratory symptoms, and they’re both spread through respiratory droplets, contaminated surfaces, or close contact.

Symptoms That Overlap:

• Cough

• Fever

• Runny or stuffy nose

• Shortness of breath

• Sore throat

• Fatigue

Given these shared symptoms, it’s easy to see why clinicians might mistake one for the other, especially without rapid diagnostic tests.

Key Differences Between Flu and HMPV

While flu and HMPV can look almost identical at first glance, experts say there are some important distinctions—especially in how symptoms progress and who gets hit hardest.

1. Onset of Symptoms

• Flu often begins suddenly, with abrupt fever, chills, and body aches.

• HMPV tends to have a gradual onset, starting with mild congestion or a dry cough that worsens over a few days.

“If you feel like you’ve been hit by a truck in a matter of hours, it’s more likely to be flu,” says Dr. Lena Romero, a pulmonologist at the National Center for Respiratory Health. “HMPV sneaks up more slowly.”

2. Wheezing and Bronchiolitis

HMPV is more likely to cause wheezing, especially in children and older adults. It can lead to bronchiolitis—inflammation of the small airways in the lungs—and in some cases, pneumonia.

Influenza can cause severe respiratory illness too, but it rarely triggers wheezing unless a secondary infection occurs.

3. Systemic vs. Respiratory Dominance

• Flu often causes systemic symptoms like intense fatigue, muscle pain, and chills.

• HMPV tends to be more localized to the respiratory system, with coughing, shortness of breath, and difficulty breathing more prominent.

Who’s at Risk?

Both viruses can affect anyone, but certain groups are more likely to experience severe illness from one over the other.

Children under 5, especially infants, are more likely to be hospitalized due to HMPV-related lower respiratory infections. Meanwhile, healthy adults may bounce back more quickly from HMPV but find the flu far more debilitating due to its intense systemic symptoms.

How Are They Diagnosed?

Because symptoms overlap, accurate diagnosis typically requires molecular testing, such as a PCR nasal swab, which can distinguish between flu, HMPV, RSV, and COVID-19.

Unfortunately, testing for HMPV is not routine in all healthcare settings. Many urgent care clinics prioritize flu and COVID testing, potentially missing HMPV cases entirely.

“In the absence of a clear diagnosis, doctors often treat symptomatically,” says Dr. Amir Qureshi, an infectious disease specialist. “But identifying HMPV is key, especially in hospitalized patients, to prevent complications.”

Treatment Options

There is no specific antiviral approved for HMPV. Treatment focuses on supportive care: rest, hydration, oxygen if needed, and medications to reduce fever and manage inflammation.

In contrast, influenza can be treated with antivirals like oseltamivir (Tamiflu) or baloxavir, especially if started within the first 48 hours of symptom onset.

This makes early diagnosis critical. Catching the flu early means you can potentially reduce severity and duration, whereas HMPV lacks this therapeutic option.

Prevention Tips for Both

Since both viruses are transmitted in similar ways, preventive strategies overlap:

• Wash hands regularly

• Avoid touching face, especially eyes and nose

• Disinfect commonly touched surfaces

• Avoid close contact with sick individuals

• Stay home if you’re sick

And of course, an annual flu vaccine is recommended for nearly everyone over 6 months of age. There’s no vaccine for HMPV—though research is ongoing—so precautions are your best defense.

When to Seek Medical Attention

Regardless of whether you suspect flu or HMPV, watch for these red flags:

• Difficulty breathing or wheezing

• High or prolonged fever

• Confusion or dizziness

• Chest pain

• Dehydration or inability to keep fluids down

In young children, look for retractions (skin pulling in around the ribs when breathing), poor feeding, or lethargy.

Final Thoughts

The flu and HMPV may look the same on the surface, but understanding the nuances in how they present can make a big difference—especially when it comes to managing symptoms and preventing complications.

If you’re feeling sick this season and symptoms aren’t resolving or are getting worse, don’t assume it’s just a cold or the flu. Ask your provider if broader viral testing—including HMPV—is available. It could mean the difference between a speedy recovery and a hospital stay.